U.S. Pat. No. 3,843,908 issued Oct. 22, 1974 to the inventor here and entitled Voltage Failure Sensing Circuit, discloses a circuit directed to generally the same purpose as the present invention of phase loss detection in a polyphase power system. That circuit, however, is dependent on the presence of an AC common line and thus is adapted for use only in conjunction with a wye configuration with the common line carried to the circuit.
Other U.S. patents directed generally to the matter of phase failure detectors are U.S. Pat. Nos.: 3,155,880; 3,377,551; 3,697,811; 3,160,786; 3,401,308; 3,736,470; 3,184,644; 3,493,783; 3,743,889; 3,248,610; 3,535,589; 3,783,341; 3,302,063; 3,600,665; 3,795,842; 3,328,606; 3,644,789; 3,848,160; 3,369,154; 3,673,502; 3,860,855; 3,866,094.